The present invention relates to a mobile scale assembly.
Commercial carriers make extensive use of interstate and intrastate highways to transport freight by vehicle to a selected destination. It is highly desirable for such commercial carriers to be able to accurately monitor both the gross vehicle weight as well as the cargo weight carried.
Gross vehicle weight is important because of highway weight limitations on transport over bridges and the like, as well as more generic restrictions that result from the amount of weight that concrete can support without damage. Cargo weight is important because a vehicle has limits on the weight that may be supported by its axles and/or wheels.
In this vein, a variety of scale assemblies have been designed to determine either gross vehicle weight, or cargo weight, or both. Such scale assemblies are preferably highly accurate. First, government regulations require that any scale assembly sold for use by commercial carriers be accurate to one pound. Second, commercial carriers want to maximize their efficiency by transporting as much cargo as possible while remaining within highway weight limitations. Because substantial fines may be levied if these limitations are exceeded, a monetary incentive exists to use the most accurate scale assemblies available.
One existing type of scale assembly, exemplified by Harris et al., U.S. Pat. No. 4,203,297, and Queen, U.S. Pat. No. 5,739,477, utilizes a large platform upon which a vehicle to be weighed may be moved. The platform rests upon a plurality of cantilevered load cells that measure the vehicle's weight. Load cells are well known in the industry and typically comprise elongate metal bars. When a load rests on the cantilevered end of a load cell, the axis of the load cell deflects and the weight of the load can be determined from the resulting strain within the load cell.
A number of disadvantages are inherent in the scale assembly just described. First, pits are usually provided to house the scale assembly and the platform in order to provide a flush surface onto which the vehicle may roll. Second, the scale assembly must be placed on a surface with adequate strength to withstand the weight placed on the load cells. These limitations restrict the mobility of the scale assembly, making it impractical to continuously monitor gross vehicle weight during transport.
Another existing design exemplified by Dojan, U.S. Pat. No. 5,635,680, employs an on-board scale assembly in which the weight of the cargo may be weighed wherever the vehicle is located. Though mobile, such on-board scale assemblies are often ineffective. First, such scale assemblies cannot effectively measure gross vehicle weight, which may vary independently of the cargo weight due to changes in fuel levels, new tires, etc. Given that gross vehicle weight must often be measured to within a pound, this shortcoming may often prove significant.
Second, continuous loading during transport may cause damage to the load cells or otherwise affect their calibration because the weight of the cargo will frequently shift or jump while the vehicle is moving. To compensate, some on-board scale assemblies utilize a hydraulic system that selectively allows the cargo to be moved onto the load cells only when the cargo is to be weighed and alternately allows the cargo to be moved from the load cells during times of transport. For such a hydraulic system to be effective, however, the scale assembly must compensate for changes in the pitch or angular orientation of the surface upon which the load rests while the hydraulic system brings the load to bear upon the load cells. Complex electronic equipment typically performs this function, but such electronic equipment is, in turn, sensitive to the environmental variations a vehicle is frequently subjected to when transporting cargo over large distances.
What is desired, then, is a mobile scale assembly that is capable of measuring both gross vehicle weight and cargo weight, and that may be used in a wide variety of locations during transport. What is further desired is a mobile scale assembly that is uncomplicated, yet accurate to within a pound and reliable after continuous use.